What is the test for an aider and abettor to be a principal in the commission of a crime?

"Principals in the commission of a crime include both the direct perpetrator of the crime and those who aid and abet the commission of the crime. [Citations.] A person aids and abets commission of a crime when, with knowledge of the perpetrator's unlawful purpose, he, by act or advice, encourages or facilitates commission of the crime with the specific intent to do so." (People v. Mejia (2012) 211 Cal.App.4th 586, 606.) However, "the aider and abettor's guilt for the intended crime is not entirely vicarious. Rather, that guilt is based on a combination of the direct perpetrator's acts and the aider and abettor's own acts and own mental state." (People v. McCoy, (2001) 25 Cal.4th 1111, 1117, some italics added.)

Thus, the mental state of a person alleged to be an aider and abettor of the charged crime "must be at least that required of the direct perpetrator. 'To prove that a defendant is an accomplice . . . the prosecution must show that the defendant acted "with knowledge of the criminal purpose of the perpetrator and with an intent or purpose either of committing, or of encouraging or facilitating commission of, the offense." [Citation.] When the offense charged is a specific intent crime, the accomplice must "share the specific intent of the perpetrator"; this occurs when the accomplice "knows the full extent of the perpetrator's criminal purpose and gives aid or encouragement with the intent or purpose of facilitating the perpetrator's commission of the crime." [Citation.]'" (People v. McCoy, supra, 25 Cal.4th at p. 1118, some italics added.)